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Comparisons of Observed Paleoclimate and Model-Based Studies of Climate Changes Over the Past Two Millennia

Comparisons of Observed Paleoclimate and Model-Based Studies of Climate Changes Over the Past Two Millennia. Michael E. Mann. Department of Environmental Sciences, University of Virginia, Charlottesville, VA. Keith Briffa Climatic Research Unit University of East Anglia, UK.

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Comparisons of Observed Paleoclimate and Model-Based Studies of Climate Changes Over the Past Two Millennia

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  1. Comparisons of Observed Paleoclimate and Model-Based Studies of Climate Changes Over the Past Two Millennia Michael E. Mann Department of Environmental Sciences, University of Virginia, Charlottesville, VA Keith Briffa Climatic Research Unit University of East Anglia, UK Collaborators: B. Adams, C. Ammann, R. Bradley; M. Cane; A. Clement, T. Delworth; M.K. Hughes, T. Osborn; P. Jones, S. Rutherford; G. Schmidt; D. Shindell; S. Zebiak CLIVAR 2004Baltimore, MD June 23, 2004

  2. Mann, M.E., Ammann, C., Bradley, R.S., Briffa, K., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures and Anomalous late 20th Century Warmth, Eos, 84, 256-258, 2003 [MODIFIED: Boreholes—Rutherford and Mann (2004); Crowley & Lowery (updated)]

  3. Greater variability in extratropics and summer! Mann, M.E., Ammann, C., Bradley, R.S., Briffa, K., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures and Anomalous late 20th Century Warmth, Eos, 84, 256-258, 2003 [MODIFIED: Boreholes—Rutherford and Mann (2004); Crowley & Lowery (updated)]

  4. Empirical Proxy-Based Climate Reconstructions

  5. Osborn, T.J., and K.R. Briffa, Comments on the paper of R. N. Harris and D.S. Chapman "Mid-latitude (30'N-60'N) climate warming inferred by combining borehole temperatures with surface air temperatures", Geophysical Research Letters, 29 (16), (45)1-2, 2002. 1. Sensitivity to scaling/calibration

  6. Mann1999(land north of 20N extractedfrom spatial reconstructions) Esper2002 Briffa2000 Jones1998 Briffa2001 www.cru.uea.ac.uk/cru/projects/soap/ From Briffa, Osborn and Schweingruber (2003) Glob Planet Change 2. Sensitivity to target region and season Comparison is difficult because each reconstruction uses a different season, region and calibration period Example shows a comparison after re-scaling every series against annual or warm-season temperature averaged over all land north of 20°N over a common 1881-1960 period

  7. 2. Sensitivity to target region and season Comparison between Briffa et al. NH extratropical warm-season NH mean temperature reconstruction with RegEM reconstruction (a) unmasked Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones, P.D., Proxy-based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Methodology, Predictor network, Journal of Climate(in revision), 2004.

  8. 2. Sensitivity to target region and season Comparison between Briffa et al. NH extratropical warm-season NH mean temperature reconstruction with RegEM reconstruction (a) unmasked (b) masked Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones, P.D., Proxy-based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Methodology, Predictor network, Journal of Climate(in revision), 2004.

  9. 2. Sensitivity to target region and season Comparison between Briffa et al. NH extratropical warm-season NH mean temperature reconstruction with RegEM reconstruction (a) unmasked (b) masked (c) based on Esper et al (2002) locations only Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K., Jones, P.D., Proxy-based Northern Hemisphere Surface Temperature Reconstructions: Sensitivity to Methodology, Predictor network, Journal of Climate(in revision), 2004.

  10. Manley/Parker Brazdil Van Engelen Wang Pfister Wang www.cru.uea.ac.uk/cru/projects/soap/ From Jones, Osborn and Briffa (2003) J Geophys Res 2. Sensitivity to target region and season Documentary evidence of change in seasonal range

  11. Model/Data Comparisons

  12. Observed warming overvarious periods ending in 2000 1991-2000 trend 1966-2000 trend 1936-2000 trend 1901-2000 trend www.cru.uea.ac.uk/cru/projects/soap/ Analysis from Tim Osborn (CRU, UEA, UK) Detection of “unusual” warming trends Compare observed trends during the 20th century with the95th percentile of pre-20th century “natural variability” trends “Unusual” warming is detectedfor cases with observed warmingexceeding all three 95th percentilesof “natural” variabilityThe temperature in this exampleis extended summer temperatureaveraged over all land north of 20N. Three estimates of “natural” variability: Reconstruction1 (from tree-rings withlow-frequency standardisation) Reconstruction2 (from tree-rings with traditional standardisation) Model (1000-yr HadCM3 control run)

  13. 1000 1200 1400 1600 1800 2000 CLIMATE FORCINGS Volcanism Solar Natural Crowley, T.J., Causes of Climate Change Over the Past 1000 Years, Science, 289 270-277, 2000.

  14. CLIMATE FORCINGS Anthropogenic Industrial Aerosols Greenhouse Gases Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

  15. Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002,doi:10.1029/2003RG000143, 2004.

  16. Observations ECHAM4-HOPE HadCM3 www.cru.uea.ac.uk/cru/projects/soap/ Data comparison from Tim Osborn (CRU, UEA, UK) Northern extratropics summer temperature Last 500 years, 10-year smoothing Tree-ring densityreconstruction

  17. European Winter Cooling During the Little Ice Age Empirical LIA winter cooling in Europe associated with an NAO trend due to solar irradiance changes, interacting w/ stratospheric atmospheric dynamics and chemistry NASA/GISS Model Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., Solar forcing of regional climate change during the Maunder Minimum, Science, 294, 2149-2152, 2001.

  18. Annual average late 17th vs late 18th Century Temperature change Proxy based reconstruction GCM Solar + Volcanic patterns Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, 4094-4107, 2003.

  19. Volcanic Radiative Summer Cooling Ensemble average summer (Jun-Aug)surface temperature response following eruption of Pinatubo. Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, 4094-4107, 2003.

  20. Volcanic Winter Dynamical Warming Ensemble average winter (Dec-Feb)surface temperature response following eruption of Pinatubo. Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, 4094-4107, 2003.

  21. Mid-Latitude Summers Greater variability? Esper, J., Cook, E.R., Schweingruber, F.H., Low-Frequency Signals in Long Tree-Ring Chronologies for Reconstructing Past Temperature Variability, Science, 295, 2250-2253, 2002.

  22. 1000 1200 1400 1600 1800 2000 Mid-Latitude Summers Greater variability?

  23. www.cru.uea.ac.uk/cru/projects/soap/ Data comparison from Tim Osborn (CRU, UEA, UK) Simulated and reconstructed changes in seasonal range ECHAM4-HOPE Thick lines = documentary record Thin lines = HadCM3

  24. www.cru.uea.ac.uk/cru/projects/soap/ Data comparison from Tim Osborn (CRU, UEA, UK) Simulated and reconstructed changes in seasonal range ECHAM4-HOPE Thick lines = documentary record Thin lines = HadCM3

  25. Volcanic Forcing of El Nino? Adams, J.B., Mann, M.E., Ammann, C.M., Proxy evidence for an El Nino-like Response to Volcanic Forcing, Nature, 426, 274-278, 2003.

  26. Theoretical mechanism for natural radiative forcing of El Nino Cane, M.A., A.C. Clement, A. Kaplan, Y. Kushnir, D. Pozdnyakov, R. Seager, S.E. Zebiak, and R. Murtugudde, Twentieth-Century Sea Surface Temperature Trends, Science, 275, 957-960, 1997.

  27. Theoretical mechanism for natural radiative forcing of El Nino Combined response to Solar +Volcanic Forcing Palymra coral isotopes (standardized to have same mean and standard deviation as Nino3 composite series) Ensemble mean Nino3 (100 realizations of CZ model) 40 year smooth Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of El Niño Over the Past 1000 Years, in revision, 2004.

  28. Theoretical mechanism for natural radiative forcing of El Nino

  29. Theoretical mechanism for natural radiative forcing of El Nino Courtesy of E.Cook

  30. CONCLUSIONS • Proxy reconstructions and model simulations both suggest that late 20th century warmth is anomalous in the context of the past 1000-2000 years • Primary source of differences between various reconstructions appear to be related to issues of seasonality and spatial representativeness • Important differences between estimates of extratropical and full (combined tropical and extratropical) hemispheric mean temperature changes in past centuries appear consistent with seasonal and spatially-specific responses to climate forcing. • Forced changes in large-scale atmospheric circulation such as the NAO, and internal dynamics related to El Nino, may play an important role in explaining regional patterns of variability and change.

  31. Observations ECHAM4-HOPE HadCM3 www.cru.uea.ac.uk/cru/projects/soap/ Data comparison from Tim Osborn (CRU, UEA, UK) Northern extratropics summer temperature Last 1000 years, 20-year smoothing Last 500 years, 10-year smoothing Tree-ring densityreconstruction

  32. www.cru.uea.ac.uk/cru/projects/soap/ Analysis from Tim Osborn (CRU, UEA, UK) Simulated changes in seasonal range over last 150 years

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